Latching sense amplifier

ABSTRACT

A latching sense amplifier includes an input stage and an output stage. The output stage is coupled to the input stage. The output stage includes a first output node, a second output node, a pull-up circuit, and a pull-down circuit. The pull-up circuit includes a first transistor, a second transistor, and a latch circuit. The first transistor is configured to pull up the first output node. The second transistor is configured to pull up the second output node. The latch circuit is configured to control the first transistor and the second transistor. The pull-down circuit includes a latch circuit configured to pull-down the first output node based on a voltage of the second output node.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This continuation application claims priority to U.S. patent applicationSer. No. 16/116,049, filed Aug. 29, 2018, which application isincorporated herein by reference in its entirety.

BACKGROUND

Sense amplifiers are used in a wide variety of applications such asanalog-to-digital converters and high-speed data communicationreceivers. The sense amplifier converts the difference of two signalsreceived as input to a higher voltage signal, such as a logic levelsignal, suitable for use in digital circuitry. The sense amplifier mayinclude latch circuitry to generate the logic level signal.

SUMMARY

A latching sense amplifier with reduced power consumption and clockloading is disclosed herein. In one example, a latching sense amplifierincludes an input stage and an output stage. The input stage includes aclocked differential amplifier. The output stage includes a first outputnode, a second output node, a pull-up circuit, and a pull-down circuit.The pull-up circuit includes a first transistor, a second transistor, athird transistor, and a fourth transistor. The second transistor iscross-coupled with the first transistor. The third transistor iscontrolled by the first transistor, and is configured to pull up thefirst output node. The fourth transistor is controlled by the secondtransistor, and is configured to pull up the second output node. Thepull-down circuit includes a fifth transistor and a sixth transistor.The fifth transistor is configured to pull down the first output node.The sixth transistor is configured to pull down the second output node.The fifth transistor and the sixth transistor are cross-coupled.

In another example, a latching sense amplifier includes an input stageand an output stage. The output stage is coupled to the input stage. Theoutput stage includes a first output node, a second output node apull-up circuit, and a pull-down circuit. The pull-up circuit includes afirst transistor, a second transistor, and a latch circuit. The firsttransistor is configured to pull up the first output node. The secondtransistor is configured to pull up the second output node. The latchcircuit is configured to control the first transistor and the secondtransistor. The pull-down circuit includes a latch circuit configured topull-down the first output node based on a voltage of the second outputnode.

In a further example, a latching sense amplifier includes an input stageand an output stage. The output stage is coupled to the input stage. Theoutput stage includes a first output node, a second output node, apull-down circuit, and pull-up circuit. The pull-down circuit is coupledto the first output node and the second output node. The pull-up circuitis coupled to the first output node and the second output node. Thepull-up circuit includes a first transistor, a second transistor, athird transistor, a fourth transistor, a fifth transistor, and a sixthtransistor. The second transistor is cross-coupled with the firsttransistor. The third transistor includes a control terminal and anoutput terminal. The control terminal is coupled to an output terminalof the first transistor. The output terminal coupled to the first outputnode. The fourth transistor includes a control terminal and an outputterminal. The control terminal of the fourth transistor is coupled to anoutput terminal of the second transistor. The output terminal of thefourth transistor is coupled to the second output node. The fifthtransistor includes a control terminal and an input terminal. Thecontrol terminal of the fifth transistor coupled to the first outputnode. The input terminal of the fifth transistor is coupled to a controlterminal of the second transistor. The sixth transistor includes acontrol terminal and an input terminal. The control terminal of thesixth transistor is coupled to the second output node. The inputterminal of the sixth transistor is coupled to a control terminal of thefirst transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 shows a schematic diagram for a double-tail sense amplifierlatch;

FIG. 2 shows a schematic diagram for a two-stage N-MOS sense amplifierlatch; and

FIG. 3 shows a schematic diagram for a latching sense amplifier inaccordance with the present disclosure.

DETAILED DESCRIPTION

Certain terms have been used throughout this description and claims torefer to particular system components. As one skilled in the art willappreciate, different parties may refer to a component by differentnames. This document does not intend to distinguish between componentsthat differ in name but not function. In this disclosure and claims, theterms “including” and “comprising” are used in an open-ended fashion,and thus should be interpreted to mean “including, but not limited to .. . .” Also, the term “couple” or “couples” is intended to mean eitheran indirect or direct wired or wireless connection. Thus, if a firstdevice couples to a second device, that connection may be through adirect connection or through an indirect connection via other devicesand connections. The recitation “based on” is intended to mean “based atleast in part on.” Therefore, if X is based on Y, X may be a function ofY and any number of other factors.

FIG. 1 shows a schematic diagram for a double-tail latching senseamplifier 100. The double-tail latching sense amplifier 100 providesgood performance with a relatively low number of transistors, butrequires a multi-phase clocking, and the output stage includes stackedP-MOS transistors that must be relatively large to provide high outputdrive. The double-tail latching sense amplifier 100 includes an inputstage 102 and an output stage 104. When a clock signal provided to thedouble-tail latching sense amplifier 100 is “low” the double-taillatching sense amplifier 100 is reset, and when the clock signal is“high” the double-tail latching sense amplifier 100 latches a valuebased on differential input signals provided to the double-tail latchingsense amplifier 100.

The input stage 102 includes a clocked differential amplifier 106 and areset circuit 108. The clocked differential amplifier 106 includes atransistor 110, a transistor 112, and a tail transistor 114. Thetransistor 110 and the transistor 112 are connected as a differentialamplifier to receive differential input signals V_(IP) and V_(IN). Thetransistor 110, the transistor 112, and the tail transistor 114 may benegative-channel (N-channel) metal oxide semiconductor field effecttransistors (MOSFETs). The tail transistor 114 is turned on when theclock signal provided to the double-tail latching sense amplifier 100 is“high” to connect the sources of the transistor 110 and the transistor112 to ground and to allow a differential voltage to develop across thedrains of the transistor 110 and transistor 112.

The reset circuit 108 is connected to the drain terminals of thetransistor 110 and the transistor 112. The reset circuit 108 includes atransistor 116, a transistor 118, and a transistor 120. The transistor116, the transistor 118, and the transistor 120 may be positive-channel(P-channel) MOSFETs. When the clock signal provided to the double-taillatching sense amplifier 100 is “low,” the transistor 116, thetransistor 118, and transistor 120 are turned on to pull up the drainterminals of the transistor 110 and the transistor 112.

The output stage 104 includes input transistor 122, input transistor124, tail transistor 126, latch transistor 128, latch transistor 130,latch transistor 132, and latch transistor 134. The input transistor122, the input transistor 124, the latch transistor 128, and the latchtransistor 130 may be N-channel MOSFETs. The tail transistor 126, thelatch transistor 132, and the latch transistor 134 may be P-channelMOSFETs. The tail transistor 126 must be relatively large to providesufficient current to quickly switch large loads. The input transistor122 and the input transistor 124 are controlled by the input stage 102.The input transistor 122 is coupled to the drain of the transistor 112,and the input transistor 124 is coupled to the drain of the transistor110. When the reset circuit 108 is active, tail transistor 126 is turnedoff, and the input transistor 122 and the input transistor 124 pull theoutput node 136 and the output node 138 of the output stage 104 toground. The tail transistor 126 is controlled by an inverted version ofthe clock signal applied to the tail transistor 114. Accordingly, thetail transistor 126 and the tail transistor 114 are turned on during thesame phase of the clock signal.

The latch transistor 128 and the latch transistor 132 are coupled toform a first inverter. The latch transistor 130 and the latch transistor134 are coupled for form a second inverter that is cross-coupled withthe first inverter to form a latch. When the tail transistor 114 and thetail transistor 126 are turned on, a differential voltage at the gatesof the transistor 110 and the transistor 112 produces a differentialvoltage at the drains of the transistor 110 and the transistor 112,which in turn drives the input transistor 122 and the input transistor124 to produce a differential voltage at the output node 136 and theoutput node 138. As the differential voltage at the output node 136 andoutput node 138 increases, one of the latch transistor 128 or the latchtransistor 130 turns on, and positive feedback within the latch causesthe output node 136 and output node 138 to swing to the power supplyrails.

FIG. 2 show a schematic diagram for a two-stage N-MOS sense amplifierlatch 200. Unlike the double-tail latching sense amplifier 100, thetwo-stage N-MOS sense amplifier latch 200 uses a single clock phase anddoes not include stacked P-channel MOSFETs, however, the output pull-updrive strength is limited. The two-stage N-MOS sense amplifier latch 200includes an input stage 202 and an output stage 204. When a clock signalprovided to the two-stage N-MOS sense amplifier latch 200 is “low” thetwo-stage N-MOS sense amplifier latch 200 is reset, and when the clocksignal is “high” the two-stage N-MOS sense amplifier latch 200 latches avalue based on differential input signals provided to the two-stageN-MOS sense amplifier latch 200.

The input stage 202 includes a clocked differential amplifier 206 and areset circuit 208. The clocked differential amplifier 206 includes atransistor 210, a transistor 212, and a tail transistor 214. Thetransistor 210 and the transistor 212 are connected as a differentialamplifier to receive differential input signals V_(IP) and V_(IN). Thetransistor 210, the transistor 212, and the tail transistor 214 may beN-channel MOSFETs. The tail transistor 214 is turned on when the clocksignal provided to the two-stage N-MOS sense amplifier latch 200 is“high” to connect the sources of the transistor 210 and the transistor212 to ground and to allow a differential voltage to develop across thedrains of the transistor 210 and transistor 212.

The reset circuit 208 is connected to the drain terminals of thetransistor 210 and the transistor 212. The reset circuit 208 includes atransistor 216, a transistor 218, and a transistor 220. The transistor216, the transistor 218, and the transistor 220 may be P-channelMOSFETs. When the clock signal provided to the two-stage N-MOS senseamplifier latch 200 is “low,” the transistor 216, the transistor 218,and transistor 220 are turned on to pull up the drain terminals of thetransistor 210 and the transistor 212.

The output stage 204 includes input transistor 222, input transistor224, tail transistor 226, latch transistor 228, latch transistor 230,latch transistor 232, latch transistor 234, and reset circuit 240. Thereset circuit 240 includes transistor 242, transistor 244, andtransistor 246. The input transistor 222, the input transistor 224, thelatch transistor 228, the latch transistor 230, and the tail transistor226 may be N-channel MOSFETs. The latch transistor 232, the latchtransistor 234, the transistor 242, the transistor 244, and thetransistor 246 may be P-channel MOSFETs. The reset circuit 240 issimilar to the reset circuit 208. When the clock signal provided to thetwo-stage N-MOS sense amplifier latch 200 is “low,” the transistor 242,the transistor 244, and the transistor 246 are turned on to pull up theoutput node 236 and the output node 238.

The input transistor 222 and the input transistor 224 are controlled bythe input stage 202. The input transistor 222 is coupled to the drain ofthe transistor 210, and the input transistor 224 is coupled to the drainof the transistor 212. The tail transistor 226 is controlled by theclock signal provided to the two-stage N-MOS sense amplifier latch 200.When the clock signal is “high” the tail transistor 226 is turned on toconnect the input transistor 222, the input transistor 224, the latchtransistor 228, and the latch transistor 230 to ground. Accordingly, thetail transistor 226 and the tail transistor 214 are turned on during thesame phase of the clock signal.

The latch transistor 228 and the latch transistor 232 are coupled toform a first inverter. The latch transistor 230 and the latch transistor234 are coupled to form a second inverter that is cross-coupled with thefirst inverter to form a latch. When the tail transistor 214 and thetail transistor 226 are turned on, a differential voltage at the gatesof the transistor 210 and the transistor 212 produces a differentialvoltage at the drains of the transistor 210 and the transistor 212,which in turn drives the input transistor 222 and the input transistor224 to produce a differential voltage at the output node 236 and theoutput node 238. As the differential voltage at the output node 236 andoutput node 238 increases, one of the latch transistor 228 or the latchtransistor 230 turns on, and positive feedback within the latch causesthe output node 236 and output node 238 to swing to the power supplyrails.

FIG. 3 shows a schematic diagram for a latching sense amplifier 300 inaccordance with the present disclosure. The latching sense amplifier 300includes some circuitry that is similar to that of the double-taillatching sense amplifier 100 or the two-stage N-MOS sense amplifierlatch 200, and the latching sense amplifier 300 provides a number ofadvantages over the double-tail latching sense amplifier 100 and thetwo-stage N-MOS sense amplifier latch 200. For example, the latchingsense amplifier 300 has lower clock loading than the double-taillatching sense amplifier 100 while providing similar performance, and incontrast to the double-tail latching sense amplifier 100, the latchingsense amplifier 300 requires only one clock phase. The latching senseamplifier 300 does not include stacked P-channel MOSFETs, which allowsthe size of the P-channel MOSFETs to be reduced.

The latching sense amplifier 300 includes an input stage 302 and anoutput stage 304. When a clock signal provided to the latching senseamplifier 300 is “low” the latching sense amplifier 300 is reset, andwhen the clock signal is “high” the latching sense amplifier 300 latchesa value based on differential input signals provided to the latchingsense amplifier 300. The input stage 302 includes a clocked differentialamplifier 306 and a reset circuit 308. The clocked differentialamplifier 306 includes a transistor 310, a transistor 312, and a tailtransistor 314. An output terminal (e.g., source terminal) 310S of thetransistor 310 is connected to an output terminal (e.g., sourceterminal) 312S of the transistor 312 to form a differential amplifierthat receives differential input signals V_(IP) and V_(IN). Thetransistor 310, the transistor 312, and the tail transistor 314 may beN-channel MOSFETs. The tail transistor 314 is turned on when the clocksignal provided to the latching sense amplifier 300 is “high” to connectthe sources of the transistor 310 and the transistor 312 to ground andto allow a differential voltage to develop across the drains of thetransistor 310 and transistor 312. The transistor 310 drives the outputnode 311 of the input stage 302, and the transistor 312 drives theoutput node 313 of the input stage 302.

The reset circuit 308 is connected to the input terminal (e.g., drainterminal) 310D of the transistor 310 and the input terminal (e.g., drainterminal) 312D of the transistor 312. The reset circuit 308 includes atransistor 316, a transistor 318, and a transistor 320. The transistor316, the transistor 318, and the transistor 320 may be P-channelMOSFETs. When the clock signal provided to the latching sense amplifier300 is “low,” the transistor 316, the transistor 318, and transistor 320are turned on to pull up the drain terminals of the transistor 310 andthe transistor 312, and the output nodes 311 and 313. The transistor 316includes an output terminal (e.g., drain terminal) 316D that isconnected to the input terminal 310D of the transistor 310. Thetransistor 318 includes an output terminal (e.g., drain terminal) 318Dthat is connected to the input terminal 312D of the transistor 312. Thetransistor 320 includes a control terminal (e.g., gate terminal) 320Gthat is connected to a control terminal (e.g., gate terminal) 316G ofthe transistor 316 and a control terminal (e.g., gate terminal) 318G ofthe transistor 318. An input terminal (e.g., source terminal) 320S ofthe transistor 320 is connected to one of the output terminal 316D ofthe transistor 316 or the output terminal 318D of the transistor 318,and an output terminal (e.g., drain terminal) 320D of the transistor 320is connected to one of the output terminal 316D of the transistor 316 orthe output terminal 318D of the transistor 318.

The output stage 304 is coupled to the input stage 302, and includes apull-down circuit 360 and a pull-up circuit 362. The pull-down circuit360 pulls the output node 336 and the output node 338 to ground, and thepull-up circuit 362 pulls the output node 336 and the output node 338 upto a power supply rail.

The pull-up circuit 362 includes input transistor 348, input transistor350, tail transistor 326, transistor 332, transistor 334, transistor352, transistor 354, transistor 356, transistor 358, and reset circuit340. The reset circuit 340 includes transistor 342, transistor 344, andtransistor 346. The input transistor 348, the input transistor 350, thetail transistor 326, the transistor 356, and the transistor 358 may beN-channel MOSFETs. The transistor 332, the transistor 334, thetransistor 342, the transistor 344, and the transistor 346 may beP-channel MOSFETs. When the clock signal provided to the latching senseamplifier 300 is “low,” the transistor 342, the transistor 344, and thetransistor 346 are turned on to pull up the control terminals (e.g., thegate terminals) 352G, 354G, 332G, and 334G of the transistor 352, thetransistor 354, the transistor 332, and the transistor 334 respectively,thereby turning off the transistor 352, the transistor 354, thetransistor 332, and the transistor 334, and disabling the transistor 352and the transistor 354 from pulling up the output node 336 and theoutput node 338.

The transistor 332 and the transistor 334 are cross-coupled to form alatch circuit 333. A control terminal (e.g., gate terminal) 332G of thetransistor 332 is connected to an output terminal (e.g., drain terminal)334D of the transistor 334. A control terminal (e.g., gate terminal)334G of the transistor 334 is connected to an output terminal (e.g.,drain terminal) 332D of the transistor 332.

The output terminal (i.e., drain terminal) 352D of the transistor 352 iscoupled to the output node 336 to pull up the output node 336. The 352Gis connected to the output terminal 332D of the transistor 332. Theoutput terminal (i.e., drain terminal) 354D of the transistor 354 iscoupled to the output node 338 to pull up the output node 338. The 354Gis connected to the output terminal 334D of the transistor 334. Thus, inthe latching sense amplifier 300, the output node 336 and the outputnode 338 are each pulled up via a single transistor.

The transistor 356 and the transistor 358 provide feedback from theoutput node 336 and the output node 338 to the transistor 332 and thetransistor 334. The control terminal (i.e., gate terminal) 356G of thetransistor 356 is coupled to the output node 336. The input terminal(e.g., drain terminal) 356D of the transistor 356 is connected to thecontrol terminal 334G of the transistor 334 to pull down the controlterminal 334G. The control terminal (i.e., gate terminal) 358G of thetransistor 358 is coupled to the output node 338. The input terminal(e.g., drain terminal) 358D of the transistor 358 is connected to thecontrol terminal 332G of the transistor 332 to pull down the controlterminal 332G.

The input transistor 348 and the input transistor 350 are controlled bythe input stage 302. The control terminal (i.e., gate terminal) 348G ofthe input transistor 348 is coupled to the output node 311 of the inputstage 302. The output terminal (i.e., source terminal) 348S of thetransistor 348 is coupled to the output terminal (i.e., source terminal)356S of the transistor 356. The input terminal (i.e., drain terminal)348D of the transistor 348 is coupled to the control terminal 332G ofthe transistor 332. The control terminal (i.e., gate terminal) 350G ofthe input transistor 350 is coupled to the output 313 of the input stage302. The output terminal (i.e., source terminal) 350S of the transistor350 is coupled to the output terminal (i.e., source terminal) 358S ofthe transistor 358. The input terminal (i.e., drain terminal) 350D ofthe transistor 350 is coupled to the control terminal 334G of thetransistor 334. The tail transistor 326 is controlled by the clocksignal provided to the latching sense amplifier 300. When the clocksignal is “high” the tail transistor 326 is turned on to connect theinput transistor 348, the input transistor 350, the transistor 356, andthe transistor 358 to ground. Accordingly, the tail transistor 326 andthe tail transistor 314 are turned on during the same phase of the clocksignal.

When the reset circuit 308 is inactive, a differential voltage at thecontrol terminals (e.g., gate terminals) 310G and 312G of the transistor310 and the transistor 312 produces a differential voltage at the inputterminals input terminal 310D and input terminal 312D of the transistor310 and the transistor 312, which in turn drives the input transistor348 and the input transistor 350 to produce a differential voltage atthe control terminal 332G of the transistor 332, the control terminal334G of the transistor 334, the control terminal 352G of the transistor352, and the control terminal 354G of the transistor 354. As thedifferential voltage increases, one of the transistor 332 and thetransistor 334 turns on, and one of the transistor 352 and thetransistor 354 turns on. Positive feedback from the output node 336 andthe output node 338 and between the transistor 332 and the transistor334 latches the state of the pull-up circuit 362.

The pull-down circuit 360 includes a transistor 322, a transistor 324, atransistor 328, and a transistor 330. The transistor 322 and thetransistor 324 are respectively coupled to the output nodes 311 and 313of the input stage 302, and controlled by the input stage 302. Thetransistor 322 includes a control terminal (e.g., gate terminal) 322Gthat is connected to the input terminal 310D of the transistor 310. Thetransistor 324 includes a control terminal (e.g., gate terminal) 324Gthat is connected to the input terminal 312D of the transistor 312. Aninput terminal (e.g., drain terminal) 322D of the transistor 322 isconnected to the output node 336 of the latching sense amplifier 300,and an input terminal (e.g., drain terminal) 324D of the transistor 324is connected to the output node 338 of the latching sense amplifier 300.

The transistor 328 and the transistor 330 are cross-coupled to form alatch circuit 331. A control terminal (e.g., gate terminal) 328G of thetransistor 328 is connected to an input terminal (e.g., drain terminal)330D of the transistor 330, the input terminal 324D of the transistor324, and the output node 338. A control terminal (e.g., gate terminal)330G of the transistor 330 is connected to an input terminal (e.g.,drain terminal) 328D of the transistor 328, the input terminal 322D ofthe transistor 322, and the output node 336.

When the reset circuit 308 is active, the transistor 322 and thetransistor 324 pull the output node 336 and the output node 338 of theoutput stage 304 to ground. When the reset circuit 308 is inactive, adifferential voltage at the control terminals (e.g., gate terminals)310G of the transistor 310 and 312G of the transistor 312 produces adifferential voltage at the input terminal 310D of the transistor 310and the input terminal 312D of the transistor 312, which in turn drivesthe transistor 322 and the transistor 324 to produce a differentialvoltage at the output node 336 and the output node 338. As thedifferential voltage at the output node 336 and output node 338increases, one of the transistor 352 and the transistor 354 turns on,which causes one of the transistor 328 and the transistor 330 to turnson and pull a corresponding one of the output node 336 and the outputnode 338 to ground. Positive feedback from the output node 336 and theoutput node 338 and between the transistor 328 and the transistor 330latches the state of the pull-down circuit 360. Thus, in the latchingsense amplifier 300, the output node 336 and the output node 338 areeach pulled down via a single transistor.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

What is claimed is:
 1. A latching sense amplifier, comprising: an inputstage comprising a clocked differential amplifier; and an output stagecomprising: a first output node; a second output node; a pull-upcircuit, comprising: a first transistor; a second transistorcross-coupled with the first transistor; a third transistor directlycoupled to the first output node, controlled by the first transistor,and configured to pull up the first output node; a fourth transistordirectly coupled to the second output node, controlled by the secondtransistor, and configured to pull up the second output node; and apull-down circuit, comprising: a fifth transistor directly coupled tothe first output node and configured to pull down the first output node;and a sixth transistor directly coupled to the second output node andconfigured to pull down the second output node; wherein the fifthtransistor and the sixth transistor are cross-coupled.
 2. The latchingsense amplifier of claim 1, wherein the pull-up circuit furthercomprises: a seventh transistor coupled to a first output node of theinput stage, and configured to control the first transistor; and aneighth transistor coupled to a second output node of the input stage,and configured to control the second transistor.
 3. The latching senseamplifier of claim 1, wherein the pull-down circuit further comprises: aseventh transistor coupled to a first output node of the input stage,and configured to pull-down the first output node; and an eighthtransistor coupled to a second output node of the input stage, andconfigured to pull-down the second output node.
 4. The latching senseamplifier of claim 1, wherein the clocked differential amplifiercomprises: a seventh transistor configured to drive a first output nodeof the input stage; an eighth transistor coupled to the seventhtransistor to form a differential pair, and configured to drive a secondoutput node of the input stage; and a reset circuit configured topull-up the first output node of the input stage and the second outputnode of the input stage.